ML19093B011
| ML19093B011 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 08/20/1977 |
| From: | Stallings C Virginia Electric & Power Co (VEPCO) |
| To: | Case E, Goller K Office of Nuclear Reactor Regulation |
| References | |
| Download: ML19093B011 (3) | |
Text
, Vepco Mr. Edson G. Case, Acting Director Office of Nuclear Reactor Regulation Attn:
Mr. Karl R. Goller, Assistant Director For Operating Reactors U. S. Nuclear Regulatory Commission Washington, D. *c.
20555
Dear Mr. Case:
TELEC0P1ER.
Serial No. 362 LQA/EAB:cwh Docket Nos:
50-280 50-281 DPR-32 DPR-37 License Nos:
During our meeting with the NRC Staff on August 19, 1977, we dis-
. cussed the opiration of th~ recirculation spray pumps under postulated loss of coolant conditions based on the results of a most recent analysis using more conservative assumptions.
We agreed to provide you with certain in-formation concerning the available ~et positive suction head (NPSH) that will exist for thise pumps and other engineered safety systems using those assumptions.
At the conclusion of our meeting, you agreed to the continued operation of these two units through August 24, 1977 on the basis of our furnishing you this letter by noon today.
Further, we agreed to furnish additional information on or. before August 24, 1977 to justify continued operation beyond that date.
Attached is a copy of a letter we have obtained, and which you have requested, from the pump manufacturer, Bingham-Willamette which de-scribes the operation of these pumps.
The most significant assumption in determining the available NPSH to the recirculation spray pumps is the distribution of energy released from the reactor coolant system between the containment atmosphere and water in the sump.
The condition which results in the potential for less than 15 feet availabl~ NPSH is a sufficiently large opening in the reactor coolant system to aH6{t the low head portion of the safety injection system to operate at ful 1 flo~*.
The ful 1 flow transfers the energy as sensible heat directly to the sump.
This causes rapid depressurization of the con-tainment and elevation of the sump water temperature which results in less than the desired NPSH.
In the event of a small break in the reactor coolant system, the higher system pressure would prevent the low head portion of the safety in-j.ection system from operation.
For this case the water suppl led by the high head pumps, while more than adequate for core cooling, would not be suff 1*-
cient to transfer the available energy to the sump ~s sensible heat.
There would be a significant amount of steam and flashing water exiting from the break, resulting in an energy distribution used i~ previous analjsis.
VIRGINIA ELECTRIC AND POWER COMPANY TO Mr. Case SHEET NO.* 2 Our analysis indicates that for a break equivalent to a six inch pipe or smaller, the reactor coolant system pressure wi 11 remain above the point necessary to prevent flow from the low head portion of the safety in-jection system.
We have considered the probability of the occurrence of a loss of coolant accident.* The probabi 1 ity that any break size* wi 11 be in excess of an equivalent six inch pipe and that. the accident will occur within any three day period during the 1 ife of the reactor is sufficiently low to justify con-tinued operation of the plant _until August *24, 1977.
This probability has been determin~d to be 0.8 x 10-6 for.~his period.
Information received from Bingham-Willamette, the recirculation spray pump manufacturer, in the attach~d letter, indicates that the pump will continue to operate toa minimum NPSH°of seven feeL At this point the flow will decrease to 2000 gpm.
When consideration is given to'.the static head of water and pipe losses* at reduced flow, the minimum available NPSH for the out.:.
side spray pumps is 8.4 feet~
A review was made of the containment pressure transient, following a design basis LOCA, considering a reduction in recirculation spray flow
- which* could result f ram a deer.ease.* in ava i lab 1 e NPSH. to the pumps.* A 11 four recirculation spray pumps were assumed to be operable and the present site cooling water temperature was used. The results indicate a containment de-press*uriza'tion time of less than one hour with. adequate cooling of the water in the sump to ensure required NPSH for the low head safety i~jection pumps in the recirculation mode.
Today, we have confirmed that. a 11 emergency core coo 1 i ng and con-tainment spray systems have been verified to be operable on bot~ Units 1 and
- 2.
As required by the techn i ca 1 sped f i cations,* periodic tests have been con-ducted recent 1 y with satisfactory results; it wi 11 not be necessary to remove any of them for further testing through August 24~ 1977.
lnstrdctions have been issued to* stat ion operat:ing personnel to verify proper a 1 ignment of a 11 pumps and valves for thesesystems duringeach operati_ng shift* *.
We will furnish you further information indicating our evaluation of the results of further computer analysis that is being carried out, and a proposal and* schedule for a permanent fix on Wednesday; August 24, 1977, for your consideration and approval to permit continued opera.tion beyond that date.
Very truly yours,
'&; ')/J?. 0/aa;~r*
- c. M. Stal 1 ings Vice President-Power Supply Attachment cc:
Mr. James P. 0 1Reilly, Director R_egion 11
8-!9-77
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